The present invention relates to a method for evaluating hydrocarbon and olefinic materials and apparatus for performing the evaluations. In particular, the present invention relates to a method and apparatus for determining non-triglycerides in edible oils and fats or oil and fat substitutes.
Edible oils and fats and substitutes therefor are commonly used by food processors, food service establishments and in the home as a food ingredient and as non-aqueous cooking media in which foods are fried. The group of fats and oils suitable for use as food ingredients are known as salad oils. The group of fats and oils suitable for use as cooking media are known as cooking oils.
Salad oils and cooking oils are directed to a variety of end uses that may require incoming inspection of the salad or cooking oil, in-use examination of the oil for control and evaluation of conformity to manufacturing or regulatory specifications, or of suitability for continued use or reprocessing.
Salad oils are primarily applied to end uses in which the salad oil is consumed directly or as part of a food formulation, in which the salad oil is not subjected to substantial heating or oxidative conditions. Cooking oils, on the other hand, are incorporated into food as a secondary effect of their being used as a heat transfer medium. Depending upon the end use, cooking oils may be used only once, such as skillet oils, and thereby receive a limited exposure to heat and oxidative conditions, or the cooking oil may be repeatedly reused, such as deep frying oils, which receive prolonged heating and oxidative exposure.
Salad and cooking oils contain or acquire a variety of non-triglyceride constituents and/or contaminants, the importance of which depend upon the particular end use of the oil. The oils may contain minor constituents from the original plant or animal tissues from which the oils were produced, such as chlorophyll or myogolobin residues. The oils may contain contaminants which are residual from the original production of the fresh oil, including desirable processing additives such as anti-oxidants, anti-foamers and crystal inhibitors and the like, as well as adulterants that may be a residual processing additive undesirable in the finished product, or a material deliberately added contrary to local regulations to dilute an expensive oil or improve the end use properties of a cheaper oil. The oil may also contain degradation products resulting from production conditions. At the end use, upon application of the oil to the food, contaminants and intentional and unintentional adulterants tend to accumulate from contact of the oil with the food and process environment. Additives may be lost by attrition. Interaction products form as a result of the reaction between and among degradation products of the oil, and with fresh oil, and introduced food materials.
Oil processors, food processors, large volume food service establishments and regulatory agencies presently employ subjective and objective techniques to perform inspections of salad and cooking oils at the site of production and consumption. The oil may be subjected to an incoming inspection to confirm the nature of the triglyceride delivered and evaluate the nature of minor constituents, contaminants, additives, adulterants and degradation products. The oil may also be subjected to in-use examination for control and evaluation of the major constituents, minor constituents, contaminants, additives, adulterants, degradation products and interaction products for conformity to manufacturing and regulatory specifications and suitability of the oil for continued use or reprocessing.
Incoming oils are inspected for level of hydrolysis, determined by measuring free fatty acid content; heat history, evaluated by color determination, which is correlative to the formation of polymeric and other condensation products; and level of oxidation, which is determined by measurement of peroxide levels, an oxidatively produced species. Incoming oils are also evaluated for their triglyceride composition, minor constituents and processing residues. The above parameters are measured for conformity to the end user's specification. Additionally, the odor and taste of incoming oils are subjectively evaluated to determine rancidity, often without reference to a control standard.
If oils such as salad oils and fresh cooking oils are in conformity with incoming inspection specifications, they are then placed in in-use bulk storage until consumed and are subjected to conditions which promote oxidation, reversion to undesirable colors and flavors, and contamination. Used cooking oils are subject to the above conditions and in addition to the formation of interaction products of the reaction between oil degradation products with fresh oil, and introduced food materials, which exceptionally increase with prolonged use. This is a concern of the end user and has a direct effect upon product shelf life, production efficiency and conformity with regulatory specifications. Extracted cooking or salad oils from foods can be tested for their properties for quality control or quality assurance purposes.
With respect to salad oils and fresh cooking oils, end use conditions promote the formation of volatile or non-volatile species, primarily free fatty acids (FFA), oxidatively produced species, and colored species. Examination of the oil for control and evaluation for conformity to manufacturing or regulatory specifications or for suitability for continued use or reprocessing can be determined by measurement of one or more of these and other species.
Once formulated, other constituents of the finished product can react with the oil to produce interaction products, primarily oxidatively produced species and condensation products which can be extracted from food products and tested for quality control or quality assurance purposes.
With respect to used cooking oils, as an oil is repeatedly used in frying, it continuously degrades in composition at the oil-water interface near the surface of the cooking food to form surfactant chemicals, hydrolytic products such as FFA, interaction products resulting from reactions with food constituents, and oil degradation products. The interaction products include oxidatively produced species and condensation products including nitrogen and sulfur containing compounds from the reaction of oil and food proteins or carmelized materials in the presence of water evolved from the frying food. The oil degradation products include condensation materials such as polymers and colored materials. The FFA combine with metals leached from food tissues and coatings, residual water hardness from sanitation activities and food ingredients to form soaps, a type of surfactant. At first the surfactants promote heat transfer at the oil-water interface at the food surface. However, with continued use, the oil further deteriorates until the surfactant chemicals reach a level at which the oil-water interfacial tension is lowered to a point where the oil interpenetrates the steam envelope from the cooking food and soaks into the food causing excessive water loss from the food surface, darkening and hardening. The oil also foams at its interface with the air, resulting in oxygen incorporation and accelerated oxidative degradation of the oil. The water loss from the food surface additionally inhibits heat penetration to the core of the food by creating a hard crust with a low thermal conductivity. Further, increased surfactant levels cause the oil to adhere to heater surfaces, which causes the oil to coke on the surfaces, thus generating colored materials and an insulating coating over the heater element surfaces, which can contribute to loss of control in a temperature versus energy process control system.
Therefore, it is desirable to maintain the surfactant level of the cooking oil within a range at which heat transfer is optimized. Once this limit is exceeded, surfactant levels may be lowered by dilution with fresh oil, by various filter aids or treatments, or the oil may be simply discarded. Therefore, it is desirable that cooking oils be routinely tested for soap or other surfactant species to determine whether an oil should be diluted, treated or discarded.
The level of soap present correlates with the general level of water-activated surfactants present and measurement of the amount of soap present in fat provides an accurate indication of the total water-activated surfactant level. The amount of soap can be determined by measuring the relative basicity of a fat sample with an alkaline indicator.
The polymers are thermal or oxygen condensation products associated with the heat history and foaming and other evidences of surfactancy of the oil and result from cross-linking of carbons from adjacent fatty acids whether free or on triglycerides or other fatty acid esters. These polymeric materials may be oxygenated or non-oxygenated and are associated with the surfactant phenomenon. Polymeric material levels may be measured by reagent indicators, the determination of which provides an indication of the in-use condition of the oil.
The majority of fatty acids free from triglycerides do not immediately form soaps, since metal ions are present in oils at the parts per million level while percentages of fatty acids are hydrolyzed from triglycerides. Oils at any given time therefore contain a certain quantity of FFA's, the levels of which correlate over a short range somewhat to the degree of degradation, although not as accurately as do measurements of soaps or total polar materials because the FFA's are intermediates in the formation of both. Stated another way, an FFA measurement is not a measurement of every FFA formed, because many FFA's further react to form soaps and other polar materials that are not detected in an FFA measurement. However, there is some utility in the determination of FFA levels, which are determined by measuring the available acidity of an oil sample with an acidic indicator.
The above species, and others present, are subclasses of non-triglycerides known as total polar materials (TPM) that form in salad and cooking oils. Many countries officially recognize TPM measurement by column chromatography as a regulatory analysis for cooking and salad oil. The previously mentioned FFA's, soaps, colored materials, polymers, degradation products, interaction products, additives, adulterants and minor constituents, all of which are not triglycerides, are collectively determined essentially quantitatively by this test. This is in contrast to individual determinations of each species, which have utility but do not provide an overall picture of the state of the oil. Because of the breadth of the materials assayed, TPM measurements are often used by regulatory agencies and manufacturers as an initial screening of an oil sample to determine if additional specific testing is necessary. Occasionally, a non-polar material such as a degradative or contaminant species may be present in a chromatographically analyzed oil sample. It would be of interest if a quick test could be devised which included these non-polar, but perhaps nutritionally important species in its assay for quality of an oil.
Methods of measuring alkalinity, TPM's and FFA's in olefinic materials such as cooking oils, and test kits employing such methods are known. U.S. Pat. No. 3,580,704 discloses a colorimetric indicator for determining the pH of motor oil in which a test paper is treated with a pH indicator and a long chain non-ionic surface active agent containing hydroxy hydrophylic groups in which the indicator is soluble, preferably an alkylaryloxy polyalkoxyalkanol such as Triton X-100. A strip of the treated paper is dipped in the oil to measure its pH.
U.S. Pat. No. 4,654,309 discloses an article for measuring the acid content of cooking oils and fats, including FFA's in which a porous support is treated with a pH indicator and a humectant dihydroxy aliphatic polyethylene glycol solvent. The strip has one or more test areas treated with a predetermined quantity of base corresponding to a known quantity of acid which must be present to neutralize the base before a color change indicating the acid quantity will occur. The pH, and hence, the fatty acid content of the oil, is measured by dipping the paper in the oil and noting the presence or the absence of a color change. Such a test, however, is destructive of the oil sample measured and does not handle well in a later, secondary examination.
U.S. Pat. No. 4,349,353 discloses a method and composition for a determination of alkaline materials such as soaps in an oil using a test solution containing a pH indicator dye and a volatile solvent that is immiscible with the oil. The solvent is used to extract alkaline substances which then react with the pH indicator in the solvent, which indicator develops a color that can be compared to a known standard to determine the pH and accordingly the degree of alkalinity and soap content of a sample.
German Patent Nos. 2,543,543 and 2,630,052 disclose methods for determining the degree of oil oxidation by dissolving the oil in a volatile alkaline alcohol solvent containing a redox indicator such as bromthymol blue, bromcresol green, cresolindophenol, thymolindophenol, bromphenol blue, thymol blue, xylenol orange, bromcresol purple, methylene violet, methylene green or patent blue.
U.S. Pat. No. 4,731,332 discloses a method and a test kit for a determination of polar substances in oil using a test solution containing indicator dye and a volatile solvent that is immiscible with the oil. The solvent is used to extract polar compounds that react with the indicator to produce a visible or fluorescent color change that is compared to a known standard to determine the amount of polar substances in the oil.
Methods using test strips are disfavored because the oil sample measured is destroyed. While extraction tests may not be destructive of the oil sample, the tests fail to accurately assay those species that are not readily extractable into water. Furthermore, once in an aqueous environment, the FFA's and alkaline species tend to neutralize each other, thereby rendering tests of either somewhat inaccurate.
The solvents in the above patents, in addition to those that are volatile, can be toxic or flammable and can present a hazard when handled in a food environment. The solvents also present a disposal problem.
A non-destructive test method and test kit that did not involve destruction of the sample or solvent partitioning of the species to be measured would be highly desirable, especially a method and test kit that was safe, non-toxic and did not present a disposal problem.